1. Field of the Invention
The present invention relates in general to a manual focusing method and system in a photographing device. More specifically, the present invention relates to a manual focusing method and system that improves focusing by capturing a window (partial image) of an image being photographed.
2. Description of the Related Art
In a photographing device for photographing a subject and storing the photographed image, focusing is an essential part of photographing to obtain a desired image of the subject. This is called focusing. The focusing can be automatically done by a photographing device. However, when the focusing is executed without involvement of the photographer (or user), a desired subject might not be accurately focused in the way the photographer wants.
This is why most of photographing devices support the automatic focusing mode as well as the manual focusing mode. In the manual focusing mode, the user executes a focusing operation by pressing manual focus buttons or rotating a manual focus ring mounted on the photographing device.
In addition, the photographing device has a display unit through which the user can see the image of a subject currently being photographed. A typically used display unit is a standard definition (SD) LCD monitor or an SD viewfinder.
Since the image shown on the display unit is merely for the user's convenience, the display unit typically does not need to have high resolution. Thus, the display unit usually displays an SD image converted from a high definition image being photographed.
However, when focusing on a subject using the manual focusing mode, the user first needs to see an image displayed on the display unit to more accurately focus on a desired subject. Therefore, it is necessary that the image shown on the display unit is sufficiently sharp to a certain extent to permit the user to manually focus properly.
Unfortunately, the SD image the display unit provides is distorted from a high resolution image captured by the camera due to some signal dropout during the image conversion process.
As a result, the user is not able to verify sharp edges in an image being photographed and therefore, has difficulty focusing accurately.
FIG. 1 is a schematic block diagram of a conventional photographing device.
As can be seen in FIG. 1, the conventional photographing device includes a lens 10, a charge-coupled device (CCD) 20, an HD camera processing unit 30, an HD codec 40, an HD media interface unit 50, media 60, a format converter 70, and a display unit 80.
The lens 10 forms the image of a subject being photographed on the CCD 20, and executes a focusing operation by moving back and forth in small amounts between the subject and the CCD 20.
The CCD 20 is a photoelectric conversion device that produces an output voltage proportional to the quantity of incident light. For instance, the CCD 20 outputs a voltage in proportion to the quantity of an incident light transmitted through the lens to the HD camera processing unit 30.
The HD camera processing unit 30 performs signal processing according to an input voltage from the CCD 20, and generates an HD signal.
The HD codec 40 compresses the HD signal generated in the HD camera processing unit 30 to be recordable in the media 60. Thus, to reproduce the HD signal from the media 60, the compressed HD signal is restored.
The HD media interface unit 50 converts the HD signal compressed by the HD codec 40 into a signal in the media recordable format. In case of reproducing the HD signal from the media, the HD media interface unit 50 performs the inversion.
The media 60 records the HD signal that is converted in the HD media interface unit 50.
The format converter 70 receives the HD signal generated in the HD camera processing unit, and converts an HD image to a downsized image with a predetermined size. For instance, if the size of the HD image is 1440*1080i, the image is downsized by the format converter 70 to 720*480i.
As a result, the produced image has a lower resolution than the HD image. The format converter 70 outputs the downsized image to the display unit 80.
The display unit 80 is formed of an SD LCD monitor 83 and/or an SD viewfinder 85, and displays the downsized image provided from the format converter 70. Then, the user views the downsized version of a photographed image on the display unit 80. By viewing the displayed image, the user can see the current focusing state or perform focusing if necessary.
However, as mentioned above, there is a problem in performing the focusing operation through the manual focusing mode, in that the user cannot focus as accurately as possible because of the lower resolution of the downsized image shown on the display unit.